Embodiments relate to the field of optical metrology, which uses video based inspection systems, coordinate measuring machines, and multisensor coordinate metrology in the measurement of form, size, and location in production and quality control. An example of such a video inspection system is described in U.S. Pat. No. 6,518,996, the disclosure of which is hereby incorporated by reference. The '996 patent discloses a video inspection apparatus including a compact Y-Z-X measurement axes system with imaging optics and a video camera mounted to the vertical Z translation axis. This vertical imaging system can take the form of a shared objective lens above the X-Y stage, followed by a zoom optical system, followed by a CCD video camera. On some systems, the objective lens can be shared with a laser range sensor system to provide a Through the Lens (TTL) laser range measurement capability on the same object being viewed by the video camera. Thus, more specifically, embodiments relate to TTL laser range sensor systems used with optical metrology systems.
Two examples of laser range sensor systems that can be deployed through the lens include triangulation laser range sensors based on the principles contained in U.S. Pat. No. 4,595,829 and conoscopic holographic sensors taught in U.S. Pat. No. 5,953,137, the disclosures of which are hereby incorporated by reference. A TTL triangulation sensor product is manufactured by Quality Vision International, Inc., Rochester, N.Y., for their inspection and measurement systems and their subsidiaries' equipment. Usually in such TTL triangulation sensors, laser light is directed to the object or surface through one half of the objective lens' entrance pupil. Here, we refer to the objective lens' “entrance” pupil since light is entering from the laser range sensor. The same pupil can also function as the “exit” pupil as will be seen below. Once the light strikes the object or surface, it is reflected and scattered, and the scattered and reflected light passes back through the other half of the objective lens previous entrance pupil, as the pupil becomes an exit pupil for the scattered and reflected light returning to the laser range sensor for detection. In conoscopic sensor products, such as that sold by Optimet or Optical Metrology, Ltd., located in Jerusalem, Israel, light passing back through the entire objective lens, now the exit pupil, is used in the detection process. Because of the different ways in which the TTL sensors use the objective lens aperture and its associated pupils, we refer to the need for the laser range sensor optical system exit pupil to fill the entrance pupil of the objective lens. For statements contained herein, and as the definition, the objective lens entrance pupil is the image of the objective lens aperture stop as “seen” by light that is entering from the laser range sensor. Neither the laser range sensor radiation beam diameter nor the reflected and scattered return beam diameters necessarily represent the exact diameter of the pupil, as the degree to which the beam should be filling the pupil depends on the particular TTL sensor used. It should also be noted that not all TTL sensor systems collimate the radiation they employ.
TTL laser probes are typically designed to be used with a specific objective lens entrance pupil size, as light enters from the laser range sensor. A typical inspection and/or measuring system 100 using a TTL laser probe arrangement 110 is shown in FIG. 1. The measuring system 100 typically includes an illumination source 105 that provides illuminating radiation to the system 100 via a beam splitter or the like 106. The probe system 110 emits a laser beam 111 toward the optical system 120, which can include a beam splitter 121, a zoom lens system 122, and an objective lens 123 that focuses radiation on an object or surface to be examined 124. The measuring system can further include an image sensor lens 125 that focuses light reflected from the object or surface to be examined 124 onto a sensor 130. The sensor 130 can be the sensor of a CCD camera 140.
As shown in FIG. 1, the beam 111 of diameter d is preferably equal to an exit pupil size of the TTL laser probe 110, and is preferably designed to fill the objective lens entrance pupil of diameter D, which must be properly filled by the radiation from the probe and the returning reflected and scattered light for optimum performance. The degree of performance sensitivity to filling of the entrance pupil depends on the particular laser probe employed. If a different objective lens with a different entrance pupil, as entered from the laser range sensor, is to be used, the laser sensor wilt operate at less than its optimum performance, particularly in height measurement sensitivity, range, resolution, and accuracy. To achieve optimum performance for a given objective lens, the laser range sensor should be redesigned to match the new diameter of the objective lens and the resulting new entrance pupil size. Redesigning the laser probe every time the objective lens' entrance pupil, as entered from the laser range sensor, is changed is costly and cumbersome. There thus exists a need for a more flexible TTL laser probe that can be used with more than one objective lens pupil size.
Embodiments provide a method of changing TTL sensor radiation exit pupil size using an expansion/contraction optical system as an adapter to properly fill an objective lens entrance pupil for which the TTL sensor was not designed. The preferred adapter is based on a Galilean optical system, though a Keplerian optical arrangement can be employed. With the adapter installed, optimum performance of the laser probe in height sensitivity, range, resolution, and accuracy can be achieved without changing the laser probe's optical system design, saving time and money. Embodiments will expand or contract the TTL sensor system radiation as desired for TTL sensor system radiation that is collimated or non-collimated.